Lady's thistle (Silbum marianum (L) Gaertn. (Carduus marianus L.) has long been knwon as a medicinal plant. From the flavolignans occurring in the fruits of this plant, R. Munster isolated a component called silybin (f. Dissertation R. Munster, Munchen, 1966). The chemical structure of this compound was elucidated by A. Pelter and R. Hansel (cf. Tetrahedron Letters, London 25 2911-2916/1968).
It is known that silybin, previously also called silymarin I, is a valuable liver therapeutic substance (cf. Federal Republic of Germany Patent Specification No. 17 67 666). A technical process for the preparation of silybin (silymarin I) is described, for example, in Federal Republic of Germany Patent Specification No. 19 23 082.
As long ago as 1974, H. Wagner, P. Diesel and M. Seitz (Arzneimittelforschung, 24 (4), 466-471) assumed, with regard to silybin, two positional isomers, namely, silybin and isosilybin. This conjecture was investigated and experimentally confirmed by A. Arnone, L. Merlini and A. Zanarotti (J. Chem. Soc., Chem. Comm., 16 696-697/1979). According to this, the known silybin consists of two different compounds, namely the compounds of the following structural formulae A and B: ##STR1## From these structural formulae, it can be seen that these compounds are positional isomers. The compound of formula A has recently been given the INN designation silibinin. This designation is also used herein for the compound of formula A.
The two-above mentioned compounds A and B have hitherto only been separated and prepared in analytical amounts and nothing is known about the pharmacological actions of the individual isomers.
In order to study the properties of these two isomers, it was necessary to have available purified quantities of each. In order to obtain this a method was developed whereby silybinin is prepared which is free of isosilybin.
Hence it is an object of this invention to provide a process for the preparation of isosilybin-free silibinin.
Once this pure silybinin was obtained, studies thereupon show that pure silibinin possesses useful pharmaceutical properties.
Hence it is a further object of this invention to obtain the pharmaceutically useful compound silybinin, and compositions containing this compound.
How these and other objects of the invention are accomplished will be seen from the Detailed Description of the Preferred Embodiments which now follows.